The present invention refers to a device for the supply of a liquid fuel to a burner member according to the preamble of claim 1.
Such fuel supply devices are known, for instance for the combustion of oil in a combustion chamber of a gas turbine device. According to conventional technique, a pump is thereby utilized, which operates at a constant speed and at a relatively high pressure dimensioned for the maximum effect of the gas turbine device. The control for adjusting the fuel quantity supplied to the combustion chamber is performed by means of a controllable throttle valve and a by-pass conduit returning surplus fuel to a drainage vessel or the like. In order to maintain the accuracy, the flow quantity supplied or the position of the throttle valve is measured, wherein the measured value is fed back.
However, such a throttling and recirculation of fuel results in a loss of the energy which has been utilized for increasing the pressure of the fuel in the fuel supply conduit. Since gas turbine devices normally operate at an effect which is lower than the maximum possible output effect, an unnecessary pump work will be performed during a not insignificant part of the operating time of the gas turbine device. In addition, the construction of such a supply device is rather complicated and expensive with a controllable throttle valve which normally is adjusted by means of an electro-hydraulic control system.
The object of the present invention is to remedy the disadvantages mentioned above and provide a fuel supply device having a higher efficiency than fuel supply devices previously known.
This object is obtained by the device initially defined, which is characterized in that said control means includes a pump driven by a motor and a control unit arranged to control the number of revolutions of said motor and thus of the pump. By controlling the number of revolutions of the motor and the pump in such a manner, the fuel supply may be controlled in a very easy and rapid manner. The number of revolutions of the motor and the pump may thus be adjusted to the pump effect required for feeding the fuel to the combustion chamber and consequently the motor will always operate at a number of revolutions which corresponds to the fuel quantity actually supplied to the combustion chamber. Furthermore, the device according to the invention provides possibilities to connect the control unit to the overall control system of the burner member of for instance a gas turbine device in an easy manner and in such a way adjust the number of revolutions of the motor to the fuel quantity required at a demanded load.
According to an embodiment of the invention, the pump includes a displacement pump. A displacement pump, for instance a piston pump, a screw pump or the like, normally has a defined relation between the number of revolutions of the pump and the flow through the pump, which enables the control of the fuel quantity supplied in an exact manner.
According to a further embodiment of the invention, the motor includes an alternating current motor. The number of revolutions of alternating current motors may be controlled in an easy manner by controlling the frequency of the motor voltage. Thereby, the motor includes an asynchronous motor and the control unit a frequency converter, advantageously a so-called static frequency converter, SFC. Such a control has a high accuracy and requires no measurement and/or feedback of the actual flow or number of revolutions of the motor.
According to a further embodiment of the invention, the control unit includes sensor members arranged to sense at least one motor parameter and an adjustment unit arranged to adjust the electric effect supplied to the motor in response to said sensed motor parameter. By means of such an adjustment unit, it is possible to provide an optimum model of the connected asynchronous motor and obtain a high control velocity, i.e. to control the number of revolutions of the motor and the pump in a very quick and accurate manner. Such a technique enables closing and acceleration of the fuel flow within 200-300 ms.
According to an advantageous application of the invention, the burner member is comprised by a gas turbine device. A calculating unit may thereby be arranged to calculate a desired fuel flow for each load condition of the gas turbine device and to calculate the desired number of revolutions of the motor for each flow, wherein the control unit is arranged to control the number of revolutions with regard to said calculations. The control may thus be based on solely the calculated value of the number of revolutions and no measurement of any parameter of the actual fuel flow is needed.
According to a further embodiment of the invention, a source is arranged to provide liquid fuel, wherein at least two fuel supply conduits extend from said source which each includes said control means. Advantageously, one of said fuel supply conduits may thereby be arranged to supply fuel to a pilot burner of said burner member and the other of said fuel supply conduits may be arranged to supply fuel to a main burner of said burner member.